Monoclonal antibodies directed against the model protein antigen, lysozyme c (HEL) are used as probes to study antibody-protein interactions and structures function relationships, and to study developmentally regulated antigens in normal and neoplastic development. The X-ray structures of two Fab-HEL complexes for 2 of these antibodies (HH5 and HH1O) have been refined, and we are now studying in detail the molecular mechanisms underlying specificity and affinity in protein-protein interactions. Site specific mutants of HH1O are being analyzed to determine the contribution of specific amino acids to antibody binding; we are in the process of cloning the rearranged genes for HH5. The gene for HEL has also been expressed in yeast by collaborators at UC Berkeley, and we are analyzing site-specific mutants to determine the contributions of individual amino acids to affinity, antigenicity, and immunogenicity. This system is currently unique in that the 3 dimensional structures of both complexes are known, and we are able to experimentally manipulate both antigen and anti- body. In addition, collaborators at Univ. Sydney have made transgenic mice which express HEL, which they recognize as a "self" protein. When these mice are crossed with transgenic mice expressing HH1O, the progeny continue to express HEL, but suppress HHlO expression. These transgenic lines provide an excellent model to investigate mechanisms regulating recognition of self, development of tolerance, and other aspects of immune regulation. The development of specificity for lysozyme from an apparently multispecific available antibody repertoire is currently being examined in detail utilizing large panels of hybridoma antibodies. In addition, monoclonal antibodies have been generated against bacterially expressed mouse c-myc protein; these antibodies will be used to purify and characterize structure-function relationships in the myc protein, applying the principles derived from the model protein studies.